Grain-Refining Carbides

Grain-refining carbides, i.e. fine particles of titanium, niobium, or vanadium carbide, keep the grain in the steel fine. During welding, they prevent the austenite grain from growing too large, which keeps the structure tough and strong. When welding, you have to make sure the heat input and cooling are right. If you get too hot or the part cools too slowly, the carbides lose their effect and you get a coarse grain. Then the part can be prone to cracking, so keep the interpass temperature within limits and don't let it cool down when doing multi-pass welds.